It’s Tori’s Riddle, developed by Tori, of course.
In this riddle series, you’ll need to explore a password for each level in order to reach the next.
Once you find out the password, modify the URL to be niwatori.io/riddle/<password> to check if it’s correct.
That’s it! The 0-th password is “start”. And welcome to Tori’s riddle.